Separation of normal paraffins from hydrocarbon mixtures using zeolitic molecular sieves



FROM HYDROCARBON CULAR SIEVES V. HAENSEL Filed March 1, 1956 SEPARATIONOF NORMAL PARAFFINS MIXTURES USING ZEOLITIC MOLE Jan. 5,

KN MN //vv/v r155: Vladimir Haense/ 8K5 A TTORA/EYS:

2,920,037 Patented J an. 5, 1960 United States Patent Oefiice SEPARATIONOF NORMAL PARAFFINS FROM HYDROCARBON MIXTURES USING ZEOLITIC MOLECULARsmvns Application March 1, 1956, Serial No. 568,809

6 Claims. (Cl. 208'310) This invention relates to a method of separatingnormal parafiins from a hydrocarbon mixture containing the same. It ismore specifically .concerned with a sorption-desorption process which isparticularly suitable for the separation of normal paraffins from ahydrocarbon mixture containing the same.

Normal paraflins find use as intermediates or raw materials in theproduction of many petro-chemicals. Normal paraffins also find wide useas solvents. While normal parafiins are not particularly desirable foruse as a motor fuel, because of their relatively low octane numbers theymay readily be isomerized to isoparaflins which have substantiallyhigher octane numbers. Since isomerization is an equilibrium reaction,it is preferred that the normal paraffins be separated from isoparaffinsbefore subjecting the normal parafiins to isomerization. In this manner,isomerization of the normal-paraflins occurs without theequilibriumrestrictions imposedby the presence of isoparaffins in the feed.

. The process of the present invention may also be used to increase theoctane number of gasolines. Forexample, a gasoline having an octanenumber of 85 F-l clear and containing normal parafiins, having anaverage octane number of zero, would have an octane improvement from 85to 94.5 by removal of these normal paraflins, on a strictly arithmeticalbasis. In the present process the normal parafiins are removed from thegasoline thereby increasing the octane number. The normal parafiinsseparated from the gasoline may be subjected to a further treatment toconvert them to aromatics and/or isoparaflins which may be blended intogasoline.

. It is an object of the present invention to separate normal paraffinsfrom a hydrocarbon mixture containing the same. i

It is another object of the present invention to provide asorption-desorption process, for the separation of normal paraflins froma hydrocarbon mixture containing the same, in which the heatrequirements for the process are kept to a minimum.

In one embodiment the present invention relates to a process whichcomprises contacting in a sorption zone a hydrocarbon mixture containingnormal paraffins with a solid sorbent-having a high sorbing power fornormal paraffins, withdrawing and recovering from said sorption zone ahydrocarbon mixture of decreased normal paraffin content, anddesorbingthe normal parafins sorbed on the solid sorbent by displacing them witha normal paraflin.

In another embodiment the present invention relates to a process whichcomprises contacting in a sorption zone a hydrocarbon mixture containingnormal paraffins and isoparafiins with "a solid sorbent having a highersorbing power for normal paraffins than for isoparaffins at atemperature within the range of from about 175 F. to'about 305 9 F.,withdrawing from said sorption zone a hydrocarbon mixture of decreasednormal parafiin content, discontinuing the introduction of thehydrocarbon mixture to said sorption zone and thereafter introducing anormal paraflin to said sorption zone, which normal parafiin selectivelyremoves the sorbed normal paraifins from said solid sorbent andrecovering the desorbed normal paraffins.

In a specific embodiment the present invention relates to a process forseparating normal paraflins from a hydrocarbon mixture containing normalparaflins, isoparaffins and aromatics which comprises introducing saidmixture to a sorption zone and therein contacting said mixture with acrystalline alumino-silicate at a temperature within the range of fromabout 175 F. to about 305 F. and a pressure within the range of fromabout 200 to about 1000 pounds per square inch gauge, withdrawing fromsaid sorption zone a hydrocarbon mixture of decreased normal paralfincontent, discontinuing the introduction of the hyrocarbon mixture to thesorption zone, thereafter introducing normal butane to said sorptionzone and displacing the sorbed normal paraffins from said crystallinealumino-silicate, reducing the pressure on said sorption zone to apressure sufiicient to vaporize the normal butane in said zone, removingnormal butane vapors therefrom and subsequently introducing ahydrocarbon mixture containing normal a the sorption zone, thehydrocarbon mixture is contacted with a solid sorbing material which hasthe power of sorbing normal paraffius from a hydrocarbon mixture such asa gasoline fraction. The effluent from the sorption zone, therefore, hasa reduced-normal parafiin content, when compared with the charge to thesorption zone. According to the process of my invention, after the solidsorbing material has picked up, or sorbed, substantial, amounts ofnormal paraflins, the introduction of the hydrocarbon mixture to thesorption zone is discontinued, and the normal paraffins are removed fromthe sorbent.

In the operation of catalytic gasoline reforming proce'sses, it has beenobserved that the product, usually called reformate, contains a smallamount of normal paraffins having relatively low octane numbers. Thepresence of these parafiins is due to the fact that under operatingconditions of reforming, the equilibrium concentration represents a fairconcentration of normal paraflins. The effect of the normal paraflins inthe reformate is to cause a substantial depression of the octane numberof the reformate. If reforming processes are operated to obtain aconversion of these normal parafiins into aromatics, or into higheroctane number isomers and lower boiling paraffins, it has been foundthat the yield-octane number improvement relationship is such thatsomewhat more than one yield percent is lost for each octane number unitgained in the range of octane numbers of the order of -95 F- l clear.This is due to the conversion of normally liquid components intonormally gaseous components. However, if the normal parafiins wereremoved the octane number would improve more favorably, for example, areformate having an octane number of 85 F-l clear and containing 10%normal parafiins, having an average octane number of zero, would haveanoctane improvement from 85 to 94.5, on a strictly' arithmetical basis.In my process the octanenumber is increased and normal paraflins arerecovered as a product. These nor mal paraflins may be isomerized toisoparaffins or dehydrogenated to aromatics and reblended intogasolines.

The charge stocks that may be treated in accordance with my inventioncomprise hydrocarbon mixtures containing normal paraffins. The mixturemay be of normal parafiins and isoparaffins; normal paraffins andcycloparafiins', normal paraflins and aromatics; normal paraftins,isoparaffins and cycloparaflins; normal paraflins, isoparaffins andaromatics; normal paraflins, cycloparaifins and aromatics; etc. It ispreferred that the charge to the sorption zone does not containhydrocarbons boiling below normal butane. The reason for this will bediscussed further in the specification. Petroleum hydrocarbons, forexample, gasolines, naphthas, etc. are mixtures containing normalparaffins, and these mixtures may be treated in accordance with thepresent invention.

The contact of the hydrocarbon mixture containing normal parafiins inthe sorption zone is with a solid sorbent. which has a selective sorbingpower for normal paraffins. The contact is for a time sufficient to sorba substantial amount of the normal parafiins present in the charge. Thesorption tower is maintained at a temperature andpressure so that thecharge is maintained in the liquid phase. As will be hereinafter furtherelaborated upon, it is preferred to maintain the temperature in thesorption zone within the range of from about 175 F. to about 305 F. Witha hydrocarbon charge mixture boiling substantially within the gasolineboiling range, the pressure in the sorption zone is within the range offrom about 200 to about 1000 p.s.i.g., to keep the charge in the liquidphase.

Any suitable solid sorbent material may be used. Preferably the solidsorbent in the sorption zone is one that has a higher sorbing power fornormal paraflins than for other hydrocarbons. Alumino-silicates such ascalcium alumino-silicate, magnesium alumino-silicate, bariumalumino-silicate, sodium alumino-silicate, potassium alumino-silicate,strontium alumino-silicate', etc. are suitable solid sorbents to usealthough they do not necessarily provide equivalent results. Crystallinecalcium aluminosilicates, which have been heated to remove the water ofhydration are preferred. These crystalline calcium alumina-silicateswhich have been heated to remove the water of hydration have porediameters of about 5.1 angstrom units, which is slightly larger than thecalculated critical diameter of normal paraflin molecules, but somewhatsmaller than the critical diameter of isoparaffins, cycloparaflins andaromatics. Thus it is possible to sorb normal paraffins from themixture.

The contact of the charge with the solid sorbent is for a timesufficient to sorb substantial quantities of the normal parafiins fromthe charge. After a substantial quantity of the normal paraflins aresorbed, the sorbed normal paraflins are removed and recovered from thesolid sorbent.

The usual procedure for removal of the sorbed normal parafiins is byheating under vacuum. Such a procedure involves a considerableexpenditure with respect to both initial installation and operatingcost. The present invention, in its preferred embodiment, provides for asimple and essential isothermal operation of the sorption and desorptioncycle. This results in a great saving in operating cost and theequipment necessary for the operation is simple and readily available.

It is thus proposed to pass a hydrocarbon mixture boiling above theboiling point of isobutane and containing normal paraflins into asorption tower which contains an absorbent capable of selectivelysorbing normal paraffins. The sorption tower is maintained at atemperature within the range of from about 175 F. to about 305 F. Thesorption tower is maintained at suflicient pressure to maintain a liquidphase and for hydrocarbon charge streams boiling substantially withinthe gasoline range pressures of from about 200 to about 1000 pounds persquare inch gauge are preferred.

. The normal paraffin which selectively removes, or displacesthe sorbednormal paraflins, may be normal buetc. although they do not necessarilyproduce equivalent results. Normal butane is a specifically preferreddisplacing agent since it is readily available. Its use has furtheradvantages, in that it is a relatively cheap refinery product, and theprocess using normal butane is tane, normal pentane, normal-hexane,normal heptane, more efficient, economical and far more simple than anyusing the higher boiling normal paraflins. A lower temperature andgenerally a lower pressure may be used with normal butane which resultsin heat saving and a saving in investment and equipment. When normalbutane is the hydrocarbon used to displace the sorbed hydrocarbon, thepressure preferably is within the range of from about 400 to about 600pounds per square inch gauge! As hereinbefore mentioned, is ispreferable to use liquid normal butane as the displacing agent in thedesorption cycle of the process, and when normal butane is used, thetemperature is preferably only slightly below the critical temperatureof normal butane and the pressure is sufficient to maintain the normalbutane as-a liquid. The critical temperature for normal butane is 305.6"F. and the critical pressure is 550 p.s.i.g. The temperature should,therefore, be below 305 F. and genarally within the 305 F. range andmore preferably fromabout 250 F. to about 305 F.

In a preferred embodiment of my invention, therefore, the sorbed normalparaffins are removed from the sorbent material by passing into contactwith the solid sorbent material a liquid normal paraffin whichselectively removes the sorbed normal parafiins from the sorbent and thesorbed normal paratiins are removed and recovered. After the sorbent haspicked up a substantial amount of normal paraffins, the sorption zonebeing maintained at 'a temperature within the range of from about 175 F;to about 305 F. and a pressure within the range of from about 400 toabout 600 pounds per square inch, the introduction of the charge isdiscontinued and liquid normal butane is introduced to the sorption zonewhich is maintained at conditions within ranges of temperature andpressure mentioned for the sorption cycle so that the normal butane ismaintained in the liquid phase. In another mode of operation, which mayreadily be adapted to a continuous type of process, the solid sorbentmaterial may be removed from the sorption zone and the treatment withthe normal butane may take place in a separate zone. The normal butanedisplaces the heavier sorbed normal parafiins and the desorbed C plussorbed paraffins are displaced from the solid sorbent and finallyrecovered.

After there is a substantial removal of. the sorbed higher boilingnormal parafiins (that is higher boiling than normal butane) by means ofthe liquid normal butane containing stream, the pressure onthe sorptiontower is lowered to permit the vaporization of the normal butane fromthe system. Since the vaporization is conducted at nearly the criticaltemperature and pressure for the normal butane stream; there isessentially no heat of vaporization, and, therefore, the unit remains atessentially the same operating temperature. Following this vaporizationof the normal butane, the charge may again be introduced to the sorptionzone and more heavier than butane, that is more C plus normal parafiinsmay be sorbed on the solid sorbent material.

In the operation wherein normal butane is displacing the C plus normalparafiins from the solid sorbent material the efliuent from the zone,which is predominantly normal paraflins, is passed to a fractionator.-In the fractionator the normal butane is fractionated from the heavierhydrocarbons and from lighter hydrocarbons when they are present. Thenormal butane recovered from the fractionator may be passed to asorption zone. to displace more C plus normal paraflins and thisrecycling of the normal butane in the process is an advantage. Ashereinbefore mentioned, normal butane may;

be present in the charge to the sorption zone and this normal butane isrecovered in the fractionation step following the sorption zoneand issubsequently used in the desorption cycle.

Using the process of my invention, therefore, the

normalparafiins may be substantially removed from hydrocarbon mixturescontaining the same. The novel features of the present invention aredescribed further in the'accom'panying diagrammatic flow drawing whichillustratesl'one specific embodiment in which the invention may bepracticed. The drawing is described in conjunction with a specificexample of the production of a high octane number motor fuel. For thepurpose of simplicity, many valves, pumps, heat exchangers, etc. havebeen omitted from the drawing since their illustration is not necessaryfor a complete understanding of the invention. I Referring now to thedrawing, a Mid-Continent straight-run gasoline fraction having aninitial boiling point of 197 F. andv an end boiling point of 398 F. andcontaining 8% normal parafiins is passed through line 1 intofractionator 2. Fractionator 2 is used since even though the chargestream has a high initial boiling point there may be some isobutane andlighter hydrocarbons dissolved in the gasoline fraction and it isdesirable to remove these by fractionation prior to contact with thesolid sorbent. In fractionator 2 the normally gaseous material, whichincludes hydracarbons containing from 1 to 4 carbon atoms per molecule,is separated from the hydrocarbon liquid comprising aromatic hydrocarbons, cycloparafiins, isoparaffins and normal paraffins. The temperature,pressure, and reflux ratio on the fractionator 2 are regulated so as toremove isobutane and lighter components from the charge in line 1 whilere taining normal butane-in the liquid bottoms.

' The gaseous material passes overhead through line 3 into cooler 4wherein a portion of the material is condensed and the entire streampasses through line 5 into receiver 6. In receiver 6 the gas phase andthe liquid phase of the overhead material separate. The gases passthrough line 7 from which they may be vented to the atmosphere orotherwise used; The fractionator 2 has heat provided thereto by reboiler10 and connecting lines 9 and 11. Fractionator 2 and receiver 6 areoperated at a sufiicient pressure to liquefy at least a portion of theoverhead material so that a liquid reflux stream is available toimprove'the operationin fractionator 2. The'liquid reflux passesfrom'receiver 6 through line 8 into. upper. portion of fractionator 2. i

The bottoms which are withdrawn from fractionator 2 through line 12contain hydrocarbons boiling above isobutane and the hydrocarbonscomprise paraflinic, isoparaffinic, cycloparaflinic and aromatichydrocarbons. The hydrocarbon mixture in line 12 may be passed througheither sorption zone 19 or sorption zone 20. In this illustration itwill be considered that the charge in line 12 was previously passedthrough sorption zone 20 and now the charge is being passed intosorption zone 19. Valve 16 in line 14 is, therefore, closed and valve 15in line 13 is maintained open. The hydrocarbon mixture in line 12continues through line 13, valve 15 and line 17 into sorption zone'19.In sorption zone 19 the hydrocarbon mixture is contacted with acrystalline calcium alumino-silicate which had previously been heated toremove the water of hydration. This sorption material sorbs normalparafiins from the hydrocarbon mixture and allows the isoparafiins,cycloparaffins and aromatics to pass from the sorption zone through line21. The sorption zone is maintained at 295 F. and 550 pounds per squareinch gauge. The liquid volume space velocity is 1.0.

The efiluent from the sorption zone 19 when withdrawn through line 21has a decreased normal paraffin content when compared with the charge inline 17. The material in line 21 continues through line 23 containingopen valve 25 and then through line 31. The material 6 in line 31consists predominantly of aromaticspcycloparaffins and isoparafiins andcontains less than 1% normal paraffins and when tested as a motor fuelit is found to be of higher octane number and has better roadperformance characteristics than the charge in line 12.

After a period of operation on this sorption cycle, the sorptionmaterial in sorption zone 19 picks up substantial amounts of normalparafins. For purposes of this illustration it will 'be considered thatthe charge stream in line 12 was passed through sorption zone 20previously and that, therefore, the solid sorption material in zone 20has substantial amounts of normal paraffins sorbed thereon. 1

Valve 35 in line 33 and valve 16 in line 14 are maintained closed and,therefore, a normal butane stream in line 50 continues through line 34,open valve 36 and line 18 into the lower portion of sorption zone 20 andthe liquid normal butane displaces the C plus sorbed normal paraffius onthe crystalline calcium aluminosilicate. During this desorbingoperation, chamber 20 is maintained at a temperature of 295 F. and apressure of 550 pounds per square inch gauge. The efliuent from chamber20 which is withdrawn through line 22 during this desorbing operation,contains predominantly normal parafiinic hydrocarbons. Liquid normalbutane is continued into chamber 20 through line 18 until substantiallyall of the C plus sorbed normal parafiins are displaced from the solidsorbent. The C plus normal paraffins continue through line 28 containingopen .valve 30 and then through line 32 into fractionator 40. I

The pressure on sorption zone 20 is then reduced to 300 pounds persquare inch gauge, thereby vaporizing the liquid normal butane inchamber 201' After this desorbing operation, the charge in line 12 maybe introduced into chamber 20 and a desorbing operation started onchamber 19. This may be accomplished by closing valve 36 in line 34 andclosing valves 15 and 30 and opening valves 16 and 26. In this operationthe charge passes through line 14, open valve 16 and line 18 intosorption zone 20. The effluent from sorption zone 20 continues throughline 22, line 24: containing open valve 26 and then through line 31 fromwhich the material has recovered as product.

Sorption zone 19 is now ready for the desorption cycle. When chamber 19is on the desorption cycle valves 15 and 25 are closed and valves 35 and29 are maintained in an open position. In this desorption cycle,theliquid normal butane in line 50 continues through line 33, open valve35, line 17 and into zone 19. The eflluent, which comprises chieflynormal paraflinic hydrocarbons during the desorption cycle, is withdrawnthrough line 21, con tinues'throu'gh line 27 containing open valve 29and then through line 32 into fractionator 40. After the pressure isreduced on zone 19 so as to vaporize the liquid normal butane, zone 19is again ready for a sorption cycle.

The normal paraffins in line 32 are introduced into fractionator 40.Fractionator 40 is operated as a debutanizer. Since fractionator 2 wasoperated so as to remove isobutane and lighter materials, normal butaneis the lightest hydrocarbon material present in the feed in line 32.Fractionator 40 has heat provided thereto by reboiler 52 and connectinglines 51 and 53. The overhead material is withdrawn from fractionator 40through line 41 and continues through cooler 42 wherein the entirenormal butane fraction is condensed and the liquid fraction in line 43is passed into overhead receiver 44. The liquid normal butane iswithdrawn from receiver 44 through line 45. A portion of this materialmay be used as reflux on column 40 and passes to an upper portion offractionator 40 through line 46. A portion of the normal butane in line47 may be withdrawn through line 48 containing valve 49. The remainderof the liquid normal butane stream continues through line 50 and is usedas the desorbing liquid. In

the first embodiment herein described wherein zone 20 was on adesorption cycle while zone 19 was on a sorption' cycle, valve 35 inline 33 was maintained closed and valve 36 was open. The liquid normalbutane material, therefore, continued through line 34, open valve 36 andline 18 into zone 20, wherein the liquid normal butane is used todisplace C and heavier paraffins.

A C plus normal paraflin stream is withdrawn from fractionator 40through line 54. This normal paraffin stream may be used directly as aproduct or may be subjected to further chemical or catalytic treatment.

The foregoing is an illustration of a specific method of operating theprocess of my invention and this illustration was described inconjunction with a specific example of the process.

I claim as my invention:

1. A process for separating a normal paraffin from a hydrocarbon mixtureboiling in the gasoline range containing said normal paraifin and ahydrocarbon selected from the group consisting of branched chain andcyclic hydrocarbons which comprises contacting said mixture at apressure sufficient to maintain the same in a substantially liquid phasewith a dehydrated metal aluminosilicate sorbent having pores of about 5Angstrom units in cross-sectional diameter, capable of selectivelysorbing normal paraflins and of rejecting branched chain and cyclichydrocarbons, withdrawing a non-sorbed liquid hydrocarbon stream ofdecreased normal paraflin content from a resulting sorbent containingsorbed normal parafiin, thereafter contacting said sorbent containingsorbed normal paraflin with a desorbent normal paramn of at least 4carbon atoms per molecule and of lower molecular weight than saidfirst-mentioned normal paraflin at a pressure at which said desorbentnormal paraflin is maintained in substantially liquid phase to thereby.displace the first-mentioned normal parafiin in the sorbent with saiddesorbent normal paraffin and withdrawing from the sorbent containingdesorbent normal paraffin a liquid mixture of said first-mentionednormal paraffin and said desorbent normal parafiin.

' 2. The process of claim 1 further characterized in that both saidsorption and desorption contacting steps are effected at substantiallythe same temperature, within the range of from about 175 to about 305 F.and at a pressure sufiicient to maintain said mixture and said desorbenthydrocarbon in substantially liquid phase.

3. The process of claim 1 further characterized in that said metalaluminosilicate is calcium aluminosilicate.

4. A process for separating normal pentane from a hydrocarbon mixturecontaining the same and isopentane which comprises contacting saidmixture with a dehydrated crystalline calcium aluminosilicate containingpores having a cross-sectional diameter of about 5 angstrorn units,capable of selectively sorbing said normal pentane while rejecting saidisopentane at a pressure at which said mixture is maintained insubstantially liquid phase, withdrawing a hydrocarbon product ofdecreased normal pentane content from the resulting calciumaluminosilicate containing sorbed normal pentane, thereafter contactingthe silicate containing sorbed normal pentane with normal butane atsubstantially the temperature maintained in the foregoing separatingstep and at a pressure at which said normal butane is maintained insubtantially liquid phase, and withdrawing from the resulting calciumaluminosilicate a stream comprising normal pentane displaced from saidsilicate by normal butane in admixture with normal butane.

5. A process for separating normal hexane from a hydrocarbon mixturecontaining the same and at least one other hydrocarbon selected from thegroup consisting of branched chain hexanes and cyclic hydrocarbons whichcomprises contacting said mixture with a dehydrated crystalline calciumalurninosilicate containing pores having a cross-sectional diameter ofabout 5 augstrom units, capable of selectively sorbing said normalhexane while rejecting said other hydrocarbon, at a pressure at whichsaid mixture is maintained in substantially liquid phase, withdrawing ahydrocarbon stream of decreased normal hexane content from the resultingcalcium aluminosilicate containing sorbed normal hexane, thereaftercontacting the silicate containing sorbed normal hexane with normalbutane at substantially the tempera-,

References Cited in the file of this patent UNITED STATES PATENTS2,306,610 Barret Dec. 29, 1942 2,376,425 Frey May 22, 1945 2,425,535Hibishman Aug. 12, 1947 2,574,434 Greentree et al. Nov. 6, 19512,586,889 Vesterdal et al Feb. 26, 1952 2,818,137 Richmond et al. Dec.31, 1957 2,818,455 Ballard et al. Dec. 31, 1957 2,859,256

Hess et al. Nov. 4,1958

1. A PROCESS FOR SEPARATING A NORMAL PARAFFIN FROM A HYDROCARBON MIXTUREBOILING IN THE GASOLINE RANGE CONTAINING SAID NORMAL PARAFFIN AND AHYDROCARBON SELECTED FROM THE GROUP CONSISTING OF BRANCHED CHAIN ANDCYCLIC HYDROCARBONS WHICH COMPRISES CONTACTING SAID MIXTURE AT APRESSURE SUFFICIENT TO MAINTAIN THE SAME IN A SUBSTANTIALLY LIQUID PHASEWITH A DEHYDRATED METAL ALUMINOSILICATE SORBENT HAVING PORES OF ABOUT 5ANGSTROM UNITS IN CROSS-SECTIONAL DIAMETER, CAPABLE OF SELECTIVELYSORBING NORMAL PARAFFINS AND OF REJECTING BRANCHED CHAIN AND CYCLICHYDROCARBONS, WITHDRAWING A NON-SORBED LIQUID HYDROCARBON STREAM OFDECREASED NORMAL PARAFFIN CONTENT FROM A RESULTING SORBENT CONTAININGSORBED NORMAL PARAFFIN, THEREAFTER CONTACTING SAID SORBENT CONTAININGSORBED NORMAL PARAFIN WITH A DESORBENT NORMAL PARAFFIN OF AT LEAST 4CARBON ATOMS PER MOLECULE AND OF LOWER MOLECULAR WEIGHT THAN SAIDFIRST-MENTIONED NORMAL PARAFFIN AT A PRESSURE AT WHICH SAID DESORBENTNORMAL PARAFFIN IS MAINTAINED IN SUBSTANTIALLY LIQUID PHASE TO THEREBYDISPLACE THE FIRST-MENTIONED NORMAL PARAFFIN IN THE SORBENT WITH SAIDDESORBENT NORMAL PARAFFIN AND WITHDRAWING FROM THE SORBENT CONTAININGDESORBENT NORMAL PARAFFIN A LIQUID MIXTURE OF SAID FIRST-MENTIONEDNORMAL PARAFFIN AND SAID DESORBENT NORMAL PARAFFIN.